An improved bolt, barrel extension and assembly

Abstract

Embodiments of the invention provide a bolt and barrel extension assembly for a gas operated firearm operable to lock by aligning bolt lugs with barrel-extension lugs and unlock by aligning bolt lugs with spaces defined between barrel-extension lugs and comprising a cam pin to rotate the bolt relative to the barrel extension, wherein the bolt provides primary extraction of a cartridge by converting rotational movement of the bolt to axial movement of the bolt with forward facing surfaces of bolt lugs bearing against rearward-facing surfaces on the barrel-extension lugs. The bolt may move to provide secondary extraction with bolt lugs aligned with spaces defined between barrel-extension lugs.

Description

[0001]An Improved Bolt, Barrel Extension and Assembly Field of the Invention This invention relates to improvements in respect of bolts of firearms and assemblies of bolts and barrel extensions. 5 Background of the Invention The cycle of operations of a firearm is well-known and includes the processes of feeding, chambering, locking, firing, unlocking, extracting, ejecting, and cocking a firearm. Locking and unlocking processes typically rely on locking lugs that engage and disengage to lock and unlock a bolt. 10 Primary extraction is an initial movement of a bolt and an associated extractor. This initial movement overcomes resistance of a spent cartridge to be removed from a firearm chamber. A range of primary extraction mechanisms are known, each placing limitations on or introducing trade-offs to the design of the rest of the firearm. Currently, few primary extraction mechanisms are known for gas operated firearms. 15 Currently also, few primary extraction mechanisms are known for firearms of the Armalite (AR) Platform. Typically, each mechanism introduces limitations or trade-offs to the firearm. It would therefore be of advantage to have a primary extraction mechanism for gas operated firearms which could address any or all of the above limitations, or at least provide the public with an alternative choice. 20 A known problem for gas operated firearms, including AR platform firearms is limited reliability of bolt lugs against lug failure. It would therefore be of advantage to have a primary extraction mechanism for AR platform firearms which could address any or all of the above limitations, or at least provide the public 25 with an alternative choice. It would therefore be of advantage to have a bolt which provides improved reliability for gas operated firearms, or at least provide the public with an alternative choice. 30 It would therefore be of advantage to have a bolt which provides improved reliability for AR platform firearms, or at least provide the public with an alternative choice. Disclosure of the Invention 35 In one aspect the invention provides a bolt and barrel extension assembly for a firearm having a forward end and a rear end the assembly having a set of bolt lugs arranged about the circumference of the bolt and a set of barrel-extension lugs arranged about the internal circumference of the barrel extension, wherein the assembly has an unlocked configuration in which the bolt lugs are aligned with spaces defined between barrel extension lugs and in which the bolt is able to move rearwardly to extract a cartridge from the barrel extension, wherein the 5 assembly has a locked configuration in which the bolt lugs are aligned with the barrel extension lugs, and wherein the bolt is able to receive an unlocking torque to actuate the bolt towards the unlocked configuration, wherein the bolt lugs define forward-facing surfaces operable to bear against cooperating reward-facing surfaces defined by the barrel-extension lugs to convert the unlocking torque to an axial component of force on the bolt towards the rear of the firearm. 10 The bolt and barrel extension assembly of any paragraph herein wherein primary extraction of a cartridge is actuated by the axial component of force provided by the forward-facing surfaces bearing against cooperating reward-facing surfaces. The bolt and barrel extension assembly of any paragraph herein operable to allow secondary extraction of a cartridge by bolt lugs being aligned with spaces between barrel-extension lugs 15 allowing the bolt to move unimpeded by the barrel extension. The bolt and barrel extension assembly of any paragraph herein wherein the forward-facing surfaces of the bolt lugs are arranged so as to bear against cooperating rear-facing surfaces of the barrel-extension lugs to cause the actuating torque to actuate the bolt to rotate and move rearwards. 20 The bolt and barrel-extension assembly of any paragraph herein wherein the bolt lugs define forward-facing surfaces operable to bear against cooperating reward-facing surfaces defined by the barrel-extension lugs to cause the bolt lugs to move to follow a helix. The bolt and barrel extension assembly of any paragraph herein wherein the forward-surface of the bolt lugs may be arranged at an angle to a plane arranged perpendicular to an axis of the 25 bolt. The bolt and barrel extension assembly of any paragraph herein wherein the cooperating rear- facing surfaces on the barrel extension lugs may be arranged at a cooperating angle to a plane arranged perpendicular to an axis of the barrel extension. The bolt and barrel extension assembly of any paragraph herein wherein said angle and 30 cooperating angle may be arranged such that movement of the bolt under the unlocking torque through a range of movement required to unlock the bolt applies the axial force suitable for primary extraction of a cartridge over an axial distance suitable for primary extraction. The bolt and barrel extension assembly of any paragraph herein wherein the forward-facing surface of the bolt lugs and cooperating rear-facing surfaces on the barrel extension lugs may 35 be arranged to cooperate by slidingly bearing against each other. The bolt and barrel extension assembly of any paragraph herein wherein the set of bolt lugs define forward-facing surfaces on the bolt lugs with a cam groove formed in the set of bolt lugs. The bolt and barrel extension assembly of any paragraph herein wherein the set of barrel extension lugs are dimensioned to be able to move along the cam groove. The bolt and barrel extension assembly of any paragraph herein wherein the set of barrel extension lugs provide cam pins which move along the cam groove. 5 The bolt and barrel extension assembly of any paragraph herein wherein the cam groove may be arranged as a helix. The bolt and barrel extension assembly of any paragraph herein wherein the set of barrel- extension lugs may comprise portions arranged so as to be operable to be received in the cam groove such that movement of the bolt lugs is defined by the helix of the cam groove. 10 The bolt and barrel extension assembly of any paragraph herein wherein the set of barrel extension lugs define rear-facing surfaces with a cam groove formed in the set of barrel extension lugs. The bolt and barrel extension of any paragraph herein wherein the set of bolt lugs are dimensioned to move along the cam groove formed in the set of barrel extension lugs. 15 The bolt and barrel extension assembly of any paragraph herein wherein a cam groove may be arranged as a helix. The bolt and barrel extension assembly of any paragraph herein wherein the set of bolt lugs may comprise portions arranged so as to be operable to be received in the cam groove such that movement of the bolt lugs under a torque towards unlocking the bolt is defined by the helix 20 of the cam groove. The bolt and barrel extension assembly of any paragraph herein wherein the angle and cooperating angle may be such that actuation of the bolt by the unlocking torque over a range of movement required to align the bolt lugs with the spaces between the barrel-extension lugs actuate the bolt to move axially with a first force provided by the unlocking torque and 25 cooperating actuation surfaces of the bolt and barrel extension. The bolt and barrel extension of any paragraph herein wherein the bolt lugs also define rearward-facing surfaces and the barrel-extension lugs define forward facing surfaces, wherein said forward rearward and forward facing surfaces conform to a helix and wherein the rearward and forward facing surfaces cooperate to actuate the bolt forwards when a torque is applied 30 towards locking the bolt. The bolt and barrel extension of any paragraph herein wherein the rearward-facing surfaces of the bolt and forward-facing surfaces of the barrel extension are dimensioned to pre-load the bolt lugs as a torque sufficient to lock the bolt is applied to the bolt. The bolt and barrel extension of any paragraph herein wherein the rearward-facing surfaces of 35 the bolt and forward-facing surfaces of the barrel extension are dimensioned to pre-stress the bolt lugs as a torque sufficient to lock the bolt is applied to the bolt. The bolt and barrel extension assembly of any paragraph herein wherein the forward-facing surface of the bolt lugs and cooperating rear-facing surfaces on the barrel extension lugs may be arranged to conform to a helix. The bolt and barrel extension assembly of any paragraph herein wherein the forward-facing 5 surfaces of the bolt lugs and the rear-facing surfaces of the barrel-extension lugs provide a cylindrical cam mechanism. The bolt and barrel extension assembly of any paragraph herein wherein the assembly is operable to have first and second modes of actuation towards extraction of a cartridge, wherein in a first mode the bolt is actuated rotationally and axially guided by the forward-facing surfaces 10 of the bolt lugs and cooperating rear-facing surfaces of barrel extension lugs towards primary extraction of a cartridge by an extractor actuated by the bolt and wherein in a second mode the bolt moves purely axially with bolt lugs aligned with spaces between barrel-extension lugs to allow secondary extraction of the cartridge. In another aspect the invention provides firearm barrel extension for use with a bolt of a firearm, 15 the barrel extension having a forward end and a rear end, the barrel extension also having a set of barrel-extension lugs arranged about the internal circumference of the barrel extension to be engaged by bolt lugs in use to lock the bolt, wherein spaces about the internal circumference of the barrel extension are defined between barrel extension lugs in which bolt lugs are able to move to allow the bolt to extract a cartridge from the barrel extension, wherein the barrel 20 extension lugs define rear-facing surfaces arranged to conform to a helix to cause bolt lugs bearing against said reward-facing surfaces to convert a torque applied to the bolt to unlock the bolt, the torque converted to an axial component of force on the bolt towards the rear of the firearm. In a further aspect the invention provides a firearm barrel having a set of barrel lugs arranged 25 about an internal circumference, wherein the lugs define a helical groove. The firearm barrel of any paragraph herein wherein the groove provides a cam groove. In a further aspect the invention provides a firearm bolt for use with a barrel extension having rear-facing surfaces which conform to a helix, the bolt having bolt lugs with forward-facing surfaces to bear against said rear-facing surfaces to convert torque on the bolt suitable to 30 unlock the bolt to an axial component of force. In a further aspect the invention provides a firearm bolt having a set of bolt lugs arranged about an external circumference, wherein the lugs define a helical groove. The firearm bolt of any paragraph herein wherein the groove provides a cam groove. The bolt of any paragraph herein having a set of bolt lugs arranged about a circumference of the 35 bolt wherein a helical cam groove is defined by the bolt lugs. In a further aspect the invention provides a bolt and barrel extension assembly for a gas operated firearm operable to lock by aligning bolt lugs with barrel-extension lugs and unlock by aligning bolt lugs with spaces defined between barrel-extension lugs and comprising a cam pin to rotate the bolt relative to the barrel extension, wherein the bolt provides primary extraction of 5 a cartridge by converting rotational movement of the bolt to axial movement of the bolt with forward facing surfaces of bolt lugs bearing against rearward-facing surfaces on the barrel- extension lugs. The bolt may move to provide secondary extraction with bolt lugs aligned with spaces defined between barrel-extension lugs. In a further aspect the invention provides a bolt and barrel extension assembly for a firearm 10 having a forward end and a rear end the assembly having a set of bolt lugs arranged about the circumference of the bolt and a set of barrel-extension lugs arranged about the internal circumference of the barrel extension, wherein the assembly has an unlocked configuration in which the bolt lugs are aligned with spaces defined between barrel extension lugs and the bolt is able to move rearwardly, and a locked configuration in which the bolt lugs are aligned with the 15 bolt lugs, and wherein the bolt comprises a bore for a cam pin operable to receive an unlocking torque to actuate the bolt towards the unlocked configuration, and wherein the bolt lugs and barrel-extension lugs are arranged to provide a cylindrical cam mechanism capable of converting the unlocking torque on the bolt to an axial force on the bolt. The bolt and barrel extension assembly of any paragraph herein wherein the bolt lug may define 20 a cam groove. The bolt and barrel extension assembly of any paragraph herein wherein the cam groove may conform to a helix. The bolt and barrel extension assembly of any paragraph herein wherein the cam groove may be arranged to conform to a spiral. 25 The bolt and barrel extension assembly of any paragraph herein wherein a barrel extension lug may define an actuation slider operable to slide through the cam groove to convert an unlocking torque to an axial force on the bolt relative to the barrel extension or barrel. The bolt and barrel extension assembly of any paragraph herein wherein the set of bolt lugs may define a cam groove extending through the set of bolt lugs. 30 The bolt and barrel extension assembly of any paragraph herein wherein the set of barrel extension lugs may define a set of actuation sliders received in a cam groove defined by the set of barrel lugs to convert the unlocking torque on the bolt relative to the barrel extension to an axial force on the bolt relative to the barrel extension. The bolt and barrel extension assembly of any paragraph herein wherein the cam groove may 35 be dimensioned to convert the unlocking torque received over a range sufficient to unlock the bolt to an axial force sufficient for primary extraction of a cartridge engaged by an extractor. The bolt and barrel extension assembly of any paragraph herein wherein the cam groove may be dimensioned to convert the unlocking torque received over a range sufficient to unlock the bolt to an axial force over a distance sufficient for primary extraction of a cartridge engaged by an extractor. 5 The bolt and barrel extension assembly of any paragraph herein wherein the assembly may have first and second modes of actuation towards extraction of a cartridge, wherein in a first mode the bolt moves rotationally and axially as guided by the cam mechanism towards primary extraction of a cartridge by an extractor associated with the bolt and wherein in a second mode the bolt moves purely axially with bolt lugs aligned with spaces between barrel-extension lugs to 10 allow secondary extraction of the cartridge. The set of barrel extension lugs may define a set of actuation sliders received in the cam groove to convert the unlocking torque on the bolt relative to the barrel extension to an axial force on the bolt relative to the barrel extension. The cam groove may be dimensioned to convert the unlocking torque received over a range 15 sufficient to unlock the bolt to an axial force sufficient for primary extraction of a cartridge engaged by an extractor. The cam groove may be dimensioned to convert the unlocking torque received over a range sufficient to unlock the bolt to an axial force over a distance sufficient for primary extraction of a cartridge engaged by an extractor. 20 The assembly may have first and second modes of actuation towards extraction of a cartridge, wherein in a first mode the bolt moves rotationally and axially as guided by the cam mechanism towards primary extraction of a cartridge by an extractor associated with the bolt and wherein in a second mode the bolt moves purely axially with bolt lugs aligned with spaces between barrel- extension lugs to allow secondary extraction of the cartridge. 25 A bolt and barrel extension assembly for a firearm operable to lock by aligning bolt lugs with barrel-extension lugs and unlock by aligning bolt lugs with spaces defined between barrel- extension lugs and comprising a cam pin to rotate the bolt relative to the barrel extension, wherein the bolt provides primary extraction of a cartridge by converting rotational movement of the bolt to axial movement of the bolt with forward facing surfaces of bolt lugs bearing against 30 rearward-facing surfaces on the barrel-extension lugs. The bolt may move to provide secondary extraction with bolt lugs aligned with spaces defined between barrel-extension lugs. The bolt may move to provide said secondary extraction under actuation of the bolt and / or bolt carrier associated with the bolt by gasses provided by propellant from a cartridge. The bolt may move to provide said secondary extraction by purely axial actuation of the bolt and / or a bolt carrier 35 associated with the bolt. A bolt and barrel extension assembly for a firearm having a forward end and a rear end the assembly having a set of bolt lugs arranged about the circumference of the bolt and a set of barrel-extension lugs arranged about the internal circumference of the barrel extension, wherein the assembly has an unlocked configuration in which the bolt lugs are aligned with spaces defined between barrel extension lugs and the bolt is able to move rearwardly, and a locked configuration in which the bolt lugs are aligned with the bolt lugs, and wherein the bolt comprises a bore for a cam pin operable to receive an unlocking torque to actuate the bolt 5 towards the unlocked configuration, and wherein the bolt lugs and barrel-extension lugs are arranged to provide a cylindrical cam mechanism capable of converting the unlocking torque on the bolt to an axial force on the bolt. A bolt lug may define a cam groove. The cam groove may conform to a helix. The cam groove may be arranged to conform to a spiral. 10 A barrel extension lug may define an actuation slider operable to slide through the cam groove to convert the unlocking torque to an axial force. The set of bolt lugs may define a cam groove extending through the set of bolt lugs. The set of barrel extension lugs may define a set of actuation sliders received in the cam groove to convert the unlocking torque on the bolt relative to the barrel extension to an axial force on 15 the bolt relative to the barrel extension. The cam groove may be dimensioned to convert the unlocking torque received over a range sufficient to unlock the bolt to an axial force sufficient for primary extraction of a cartridge engaged by an extractor. The cam groove may be dimensioned to convert the unlocking torque received over a range 20 sufficient to unlock the bolt to an axial force over a distance sufficient for primary extraction of a cartridge engaged by an extractor. The assembly may have first and second modes of actuation towards extraction of a cartridge, wherein in a first mode the bolt moves rotationally and axially as guided by the cam mechanism towards primary extraction of a cartridge by an extractor associated with the bolt and wherein in25 a second mode the bolt moves purely axially with bolt lugs aligned with spaces between barrel- extension lugs to allow secondary extraction of the cartridge. A bolt and barrel extension assembly for a firearm having a forward end and a rear end the assembly having a set of bolt lugs arranged about the circumference of the bolt and a set of barrel-extension lugs arranged about the internal circumference of the barrel extension, wherein 30 the assembly has an unlocked configuration in which the bolt lugs are aligned with aligned with spaces defined between barrel extension lugs and the bolt is able to move rearwardly to extract a cartridge from the barrel extension, and a locked configuration in which the bolt lugs are aligned with the bolt lugs, and wherein the bolt comprises a bore for a cam pin operable to provide an unlocking torque applied to the bolt to actuate the bolt towards an unlocked 35 configuration, wherein the bolt lugs define forward-facing surfaces operable to bear against cooperating reward-facing surfaces defined by the barrel-extension lugs to convert the unlocking torque to an axial force on the bolt towards the rear of the firearm. The forward-facing surface of the bolt lugs and cooperating rear-facing surfaces on the barrel extension lugs may convert rotational torque to axial force. The forward-facing surface of the bolt lugs may be arranged at an angle to a plane arranged perpendicular to an axis of the barrel extension. 5 The cooperating rear-facing surfaces on the barrel extension lugs may be arranged at a cooperating angle to a plane arranged perpendicular to an axis of the barrel extension. Said angle and cooperating angle may be arranged such that movement of the bolt under the unlocking torque through a range of movement required to unlock the bolt applies the axial force suitable for primary extraction of a cartridge over an axial distance suitable for primary 10 extraction. The forward-surface of the bolt lugs and cooperating rear-facing surfaces on the barrel extension lugs may be arranged to cooperate by slidingly bearing against each other. The set of bolt lugs may define forward-facing surfaces on the bolt lugs with a cam groove formed in the set of bolt lugs. 15 The cam groove may be arranged in a helix. The set of barrel-extension lugs may comprise portions arranged so as to be operable to be received in the cam groove such that movement of the bolt lugs is defined by the helix of the cam groove. Said portions arranged so as to be operable to be received in the cam groove may be cams. 20 The angle and cooperating angles may be such that actuation of the bolt by the unlocking force over a range of movement required to align the bolt lugs with the spaces between the barrel- extension lugs may actuate the bolt to move axially with a first force provided by the unlocking torque and cooperating actuation surfaces of the bolt and barrel extension. The forward-surface of the bolt lugs and cooperating rear-facing surfaces on the barrel 25 extension lugs may be arranged to conform to a helix. In one aspect the invention provides a firearm bolt and firearm barrel extension assembly having a locked configuration and unlocked configuration, wherein locking lugs on the bolt and locking lugs of the barrel extension are arranged so as to allow the bolt to be threaded towards 30 the rear of the firearm as the bolt is rotated relative to the barrel extension towards an unlocked configuration. The locking lugs on the bolt and locking lugs of the barrel extension may be arranged to provide mechanical advantage for axial movement of the bolt as it is rotated relative to the barrel extension towards an unlocked configuration. 35 In one aspect the invention provides a firearm bolt having a set of locking lugs arranged along a helix. The set of locking lugs may be arranged so as to cause the bolt to translate as it rotates. The set of locking lugs may be arranged so as to cause the bolt to translate rearwardly with respect to the firearm as it rotates towards an unlocked configuration. The translation may actuate an extractor associated with the bolt. The translation may have mechanical advantage with respect to said rotation. The mechanical advantage may be defined by the helix. The 5 mechanical advantage may be defined by a pitch of the helix. In one aspect the invention provides a firearm bolt having lugs arranged in pairs about a periphery of the bolt, wherein each lug in a pair is aligned with the other in the pair along the periphery of the bolt. 10 In one aspect the invention provides a barrel extension of a firearm the barrel extension formed so as to guide lugs of a bolt in a helical path. In one aspect the invention provides a barrel extension of a firearm the barrel extension formed 15 so as to receive lugs of a bolt arranged in a helix on the bolt. In one aspect the invention provides an assembly of a bolt and barrel extension of a firearm, the assembly having barrel lugs formed on the barrel extension and having bolt lugs formed on the bolt, the barrel extension lugs and bolt lugs being arranged engage to lock the bolt in the barrel 20 extension when the bolt is rotated relative to the bolt extension in a first sense and to disengage to allow the bolt unlock when the bolt is rotated in a second sense, wherein the bolt lugs have actuation surfaces formed thereon said actuation surfaces arranged bear against cooperating surfaces on barrel extension lugs so as to actuate the bolt along the axis as the bolt is rotated.The bolt lugs and barrel lugs may be arranged to allow the bolt to be threaded towards 25 the rear of the firearm as the bolt is rotated relative to the barrel extension towards an unlocked configuration. The assembly may comprise a bore for a cam pin to move the bolt rotationally. Said cooperating surfaces on the barrel extension lugs may conform to a helix having the same geometry as the helix of the bolt lugs. 30 The assembly may comprise a cartridge extractor connected to the bolt to be actuated by the bolt, wherein actuation of the bolt by the actuation surfaces when the bolt is rotated actuates the cartridge extractor. The helix of the bolt lugs and / or the helix of the barrel extension lugs may have a geometry such that rotation of the bolt through a range of angles required to release the bolt from the barrel 35 extension to unlock the bolt causes said actuation of the bolt over a distance suitable for primary extraction of a cartridge. The helix of the bolt lugs and / or the helix of the barrel extension lugs may have a geometry arranged such that rotation of the bolt towards releasing the bolt lugs from barrel extension lugs provides mechanical advantage for rearward movement of the bolt to perform primary 40 extraction. In one aspect the invention provides a barrel extension of a firearm for use with a bolt, the barrel extension having barrel extension lugs arranged to co-operate with bolt lugs to lock the bolt when the bolt is rotated relative to the bolt extension in a first sense to a locked orientation and to release the bolt from the barrel extension when the bolt is rotated in a second sense to an 5 unlocked orientation, wherein the barrel lugs have actuation surfaces formed thereon, wherein the actuation surfaces on the barrel lugs are arranged to cooperate with actuation surfaces on the bolt lugs to actuate the bolt along the axis as the bolt is rotated in the second sense. Said rotation may be through a defined range of angles. In one aspect the invention provides a bolt of a firearm for use with a barrel extension of a 10 firearm, the bolt having bolt locking lugs arranged to engage barrel lugs on the barrel extension to retain the bolt in the barrel extension when the bolt is rotated relative to the bolt extension in a first sense to lock the bolt and arranged to disengage to allow the bolt to be removed from the barrel extension when the bolt is rotated in a second sense to unlock the bolt, wherein the bolt locking lugs have actuation surfaces formed thereon and wherein the actuation surfaces are 15 arranged so as bear against cooperating surfaces on the barrel lugs to actuate the bolt along an axis of the bolt as the bolt is rotated on said axis in the second sense. The actuation surfaces of the bolt may conform to a helix. The helix may be oriented to have a central axis aligned with a central axis of the bolt. The actuation surfaces of a set of said barrel lugs may conform to a helix. The helix of barrel 20 lugs may be the helix of the bolt lugs when the bolt is positioned so that the actuation surfaces of the bolt lugs bearing against the actuation surfaces of the barrel lugs. This may cause the actuation surfaces of the bolt lugs to move along the helix. The helix defines a component of axial movement along a central axis for a component of rotational movement about the central axis. 25 In one aspect the invention provides a bolt of a firearm, the bolt having two or more locking lugs which define respective two or more surfaces that conform to a helix. The helix may be common to the two or more surfaces. The helix may have a central axis parallel to a central axis of the bolt. Said surfaces moving along the helix will move rotationally about the central axis and also move along the axis. Said surfaces bearing against surfaces on a cooperating barrel extension 30 while the bolt is rotated will actuate the bolt along the axis. Said actuation may have a component of movement along the axis. Said actuation may comprise helical movement of bolt locking lugs with a central axis of the helix being parallel with the axis of the bolt. This may cause the bolt to move with a component of movement in the axis of the bolt when the bolt is rotated. 35 Said component of movement may be actuated by cooperating actuation surfaces may be in a rearward direction towards the rear of the firearm. The assembly may comprise an extraction clip arranged to engage a cartridge to move it rearwardly as the bolt moves rearwardly. The component of movement may be over a distance adapted for primary extraction of the round. Primary extraction may be a primary movement to dislodge a round prior to a secondary movement of the bolt to remove the round entirely. Primary extraction may be a primary movement to dislodge a cartridge retained in a chamber of 5 the firearm by elastic deformation. Primary extraction may be a primary movement to dislodge a cartridge retained in a chamber of the firearm by hydrostatic forces. Primary extraction may be a primary movement to dislodge a cartridge retained in a chamber of the firearm by a combination of elastic deformation and hydrostatic forces. 10 This distance for primary extraction may be actuated by rotation of the bolt sufficiently to move the bolt lugs from locked positions in which the bolt is locked in the barrel extension for firing and unlocked positions in which the bolt is released from the barrel extension and free to move axially. This distance may be actuated by rotation of the bolt by 22.5 degrees. 15 This distance may be actuated by rotation of the bolt sufficiently to release a locked AR platform bolt from an AR bolt extension. The actuation surfaces may actuate the bolt along a central axis of the bolt as it is rotated so as to provide mechanical advantage to the bolt to dislodge a cartridge from a chamber of the firearm with an extractor that is actuated by the bolt. 20 The barrel extension may have cooperating actuation surfaces arranged to cooperate with the actuation surfaces as the bolt is rotated. This may be rotation in the second sense. This may be rotation towards release of the bolt. The actuation surfaces of the bolt lugs and cooperating actuation surfaces of the barrel lugs 25 may conform to a helix. The actuation surfaces of the bolt lugs and cooperating actuation surfaces of the barrel lugs may define a helix. A juncture between actuation surfaces of the bolt lugs and cooperating actuation surfaces of the barrel lugs may conform to a helix. 30 Rotation of the bolt relative to the barrel extension may cause a bolt locking lug to move along a helix when moved relative to the barrel extension with actuation surfaces and cooperating actuation surfaces in contact. The helix may be oriented to have a central axis aligned with the central axis of the bolt. A helix oriented to be aligned with the central axis of the bolt will define a length of movement along the central axis for a degree of rotation about the central axis. A helix oriented to be aligned with the central axis of the bolt will define a rate of movement along the axis for a rate or rotation about the axis. 5 The actuation surfaces of the barrel lugs and bolt locking lugs may conform to the same helix when the actuation surfaces of barrel locking lugs and bolt locking lugs are in contact. The helix may have a pitch which is determines a length of movement for the bolt as the bolt is rotated over a range of angles required to disengage the lugs. The helix may have a pitch which is determines a length of movement for the bolt as the bolt is 10 rotated over a range of rotation sufficient to disengage the lugs, wherein the length of movement is selected as optimal for primary extraction of a cartridge. The helix may have a pitch defining a rate of distance of axial actuation for degrees of rotation of the bolt relative to the barrel extension. The barrel locking lugs and bolt locking lugs may be arranged to disengage with approximately 15 22 degrees of rotation. The barrel locking lugs and bolt locking lugs may be arranged to disengage with 22.5 degrees of rotation. An actuation surface on the barrel lugs may face rearward with respect to the firearm. Alternatively, barrel locking lugs may comprise sets of two of more barrel locking lugs. 20 An actuation surface on the barrel lugs may face forward with respect to the firearm. Each bolt locking lug may define two actuation surfaces. Alternatively, the barrel locking lugs may comprise sets of two of more barrel locking lugs. A bolt locking lug may be substantially elongate with a transverse groove formed in it to provide a first actuation surface. A forward-facing surface of a bolt locking lug may provide a second 25 actuation surface. The forward-facing surface may be a surface substantially transverse to the central axis of the bolt. The barrel locking lug and the bolt locking lugs may be arranged to engage to bear the impulse of recoil of a round being fired. The barrel locking lugs and bolt locking lugs may be arranged to lock to bear the impulse of recoil by having one or more locking surfaces each arranged to 30 cooperate with a respective cooperating locking surface. The barrel locking lug and bolt locking lugs may be arranged so that the locking surfaces disconnect as rotation of the bolt towards disengagement. A locking surface may be located opposite and distal to an actuation surface on a respective locking lug on a bolt. A locking surface may be located oppose an actuation surface on a pair of locking lugs on a barrel extension. 5 The barrel extension may have lugs at each of a number of locations about the internal circumference of the barrel extension. The barrel extension may have two or more lugs at each said location about the internal circumference of the barrel extension. The bolt may have lugs at each of a number of locations about the external circumference of the 10 bolt. The bolt may have two or more lugs at each said location about the external circumference of the barrel extension. A lug may be formed by Computer Numerical Control (CNC) machining of a bolt or barrel extension. 15 A lug may be formed by milling of a bolt or barrel extension. A barrel extension may have a region at a location on the internal circumference of the barrel extension defining a space for a round-extraction device operable to extract a round. The round- extraction device may be a round-extraction clip. A space for a round-extraction device may be dimensioned to allow access for a machining tool 20 to form the barrel lugs. The barrel locking lugs may be arranged in a helical configuration. The bolt locking lugs may be arranged in a helical configuration. The barrel locking lugs and bolt locking lugs may cooperate by guiding the bolt in a helical movement when the bolt moves relatively towards the rear of the firearm. 25 The helical configuration may have a pitch. The assembly may comprise a device arranged to engage a round to extract a cartridge of the round from the barrel extension as the bolt moves rearward. The device arranged to engage a cartridge may be an extractor. The extractor may be arranged to engage a rim formed on the cartridge to pull the cartridge rearward as the bolt moves rearward. 30 The pitch may be arranged to cause a defined range of axial movement of the bolt when the bolt is rotated about it’s axis by a range of rotation required to move the lugs from an engaged configuration in which the lugs are engaged for firing a round to a disengaged configuration in which the lugs are disengaged to allow the bolt to move axially. In another aspect the invention provides a method of fabrication of a bolt comprising machining a cam groove in a bolt locking lug. The cam groove may provide a surface which conforms to a helix. The helix may have a central axis extending along a central axis of the bolt. The method may comprise machining the cam groove so as to provide a surface which conforms to a helix. 5 The method may comprise machining a cam groove in each of multiple bolt locking lugs. The method may comprise machining each of multiple lugs so as to provide surfaces on said multiple lugs that conform to a helix in common to said multiple lugs. The method may comprise machining the cam groove so as to provide said surfaces facing approximately to the rearward of a firearm in which the bolt is to be used. Said approximate facing may be perpendicular to a 10 central axis of the bolt offset by the helix. Said offset may be in two degrees of freedom. Said offset may be in two axes. Other aspects of the invention may provide a method of manufacture of a barrel extension comprising machining a barrel locking lug so as to provide a surface which conforms to a helix oriented with a central axis along a central axis of the barrel extension. Said central axis of the 15 barrel extension may be the axis in which an end of a bolt received in the barrel extension 3 would extend. The barrel extension and bolt may be of a gas operated firearm in which gas from a round actuates a bolt carrier to actuate the bolt towards the rear of the firearm. Alternatively to any one or more of the paragraphs above, actuation surfaces arranged to 20 actuate the bolt along a central axis of the bolt may be provided other than on bolt lugs. In a further aspect the invention provides a bolt and barrel extension assembly wherein the bolt has lugs configured to thread into the barrel extension to unlock the bolt from the barrel extension. The barrel extension may comprise a set of lugs to cooperate with the bolt lugs to allow said threading. 25 In a further aspect the invention provides a bolt and barrel extension assembly wherein the bolt has a set of lugs configured to thread into the barrel extension to unlock the bolt from the barrel extension. The barrel extension may comprise a set of lugs to cooperate with the bolt lugs to allow said threading. In a further aspect the invention provides a bolt and barrel assembly wherein the bolt has lugs 30 configured to thread into the barrel extension to unlock the bolt from the barrel extension. The barrel may comprise a barrel extension. The barrel extension may comprise a set of lugs to cooperate with the bolt lugs. In some embodiment the bolt lugs and barrel lugs of any paragraph above are arranged to allow the bolt to be threaded forwards as the bolt is rotated to lock so. In this embodiment the 35 threading action creates a tight fit or minimised tolerance between the bolt lugs and barrel extension lugs to mitigate the bolt tilting with respect to the barrel extension. In these embodiments load caused by locking and / or recoil is spread evenly across a set of bolt lugs. In these embodiments uneven load across a set of locking lugs is mitigated. In some embodiments the bolt of any paragraph above comprises bolt lugs which are arranged in a helix on the bolt. In some embodiments the barrel extension comprises barrel extension lugs which define a helical groove. In some embodiments the bolt of any paragraph above comprises barrel extension lugs which 5 are arranged in a helix around an internal circumference of the barrel extension. In some embodiments the bolt of any paragraph above comprises bolt lugs which define a helical groove. In this embodiment barrel extension lugs arranged in a helix may be received in the groove.In one aspect the invention provides an assembly of a bolt and barrel extension of a firearm, the assembly having barrel lugs formed on the barrel extension and having bolt lugs 10 formed on the bolt, the barrel extension lugs and bolt lugs being arranged engage to lock the bolt in the barrel extension when the bolt is rotated relative to the bolt extension in a first sense and to disengage to allow the bolt unlock when the bolt is rotated in a second sense, wherein the bolt lugs have actuation surfaces formed thereon said actuation surfaces arranged bear against cooperating surfaces on barrel extension lugs so as to actuate the bolt along an axis of 15 the bolt as the bolt is rotated. The actuation surfaces of the bolt lugs may be 3-dimensional surfaces which are perpendicular to a central axis of the bolt in a first dimension and at an angle to the central axis in a second dimension. The surface may face approximately forward in respect to the bolt when in use. Said actuation surface will present a surface at a cross-section of the bolt along the central axis of 20 the bolt which moves forward as the bolt is rotated in the second sense. This may force the actuation surface at said cross-section against any cooperating surface provided on a barrel extension lug. The actuation surface being perpendicular to a central axis of the bolt in a first dimension and at an angle to the central axis in a second dimension may extend linearly at said angle. 25 Alternatively actuation surface being perpendicular to a central axis of the bolt in a first dimension and at an angle to the central axis in a second dimension may extend as a section of thread. Alternatively, actuation surface being perpendicular to a central axis of the bolt in a first dimension and at an angle to the central axis in a second dimension may extend as a truncated 30 thread. Alternatively, actuation surface being perpendicular to a central axis of the bolt in a first dimension and at an angle to the central axis in a second dimension may extend as a section of a helix. Alternatively, actuation surface being perpendicular to a central axis of the bolt in a first 35 dimension and at an angle to the central axis in a second dimension may extend as a truncated helix. Said actuation surfaces of a set of actuation surfaces may conform to a helix having a central axis aligned with a central axis of the bolt. Said actuation surfaces of a set of actuation surfaces may conform to a thread having a central axis aligned with a central axis of the bolt. 5 Alternatively said actuation surfaces of a set of bolt lugs may be at approximately the same place along the the bolt. Such surfaces will each conform to a different helix or thread. Here ‘along’ refers to a position on the central axis. Alternatively, said actuation surfaces may each be at the same angle to the central axis. Said actuation surfaces may each be at the same position along the bolt. Here ‘along’ refers to a 10 position on the central axis. The actuation surfaces may be provided by a groove formed in an elongate blank for a lug. The actuation surfaces may be provided by a groove defined by an elongate lug. A barrel extension lug may provide may provide an actuation lug which fits in the groove in the bolt lugs. 15 A barrel extension lug may provide an actuation lug which provides a surface suitable for an actuation surface of a bolt lug to bear against. For example, the cross-section of the bolt lug along the axis of the bolt which moves forward as the bolt is rotated in the second sense may force the bolt rearwardly. The angle of the actuation surface may be arranged such that the degree of said forward movement of the bolt lug surface relative to the bolt for a degree of 20 rotation acting against a cooperating rearward-facing surface of a barrel extension lug causes the bolt to move suitable for primary extraction of a cartridge as the bolt is rotated sufficiently to unlock the bolt. For example a 22.5 degree rotation may be required to inlock the bolt and rearward movement of the bolt may as defined by a 5 to 10 degree pitch on the bolt lug surface. As used herein the terms ‘threaded’ or ‘threading’ refer broadly to moving as defined by a thread 25 and includes both threading and unthreading in the sense that a nut may be threaded onto a bolt or threaded off a bolt. As used herein the term ’barrel extension’ is an extension to a rearward end of a firearm barrel which provides features to lock a bolt in place so as to maintain a chamber of the firearm closed for firing a round located in the chamber. 30 As used herein a ‘barrel locking lug’ is a feature formed in a barrel extension to engage a bolt locking lug to lock an end of a bolt in the barrel extension. As used herein a ‘bolt locking lug’ is a feature formed in a bolt extension wherein the feature engages a barrel locking lug to lock an end of a bolt in the barrel extension. A lug may be a protrusion. Alternatively, a lug may be a recess. As used herein the term ‘helix’ refers to a smooth space curve with tangent lines at a constant angle to a fixed , typically central, axis. As used herein the term ‘forward’ may be towards the front of the firearm in a direction a projectile would be fired. 5 As used herein, the term ‘rearward’ may be towards the rear of the firearm distal from the end of a firearm where a projectile would be fired from. As used herein the terms ‘locking’, ‘lock’ and similar and terms ‘extracting’, ‘extract’ and similar refer to processes in the cycle of operations of a firearm, which includes the processes of feeding, chambering, locking, firing, unlocking, extracting, ejecting, and cocking. The term 10 ‘extraction’ specifically refers to the removal of the spent cartridge case from the chamber. As used herein the term ‘release’ refers to the process of unlocking. As used herein the term ‘locking lug’ refers broadly to a feature which provides a locking function for a bolt in the locking process of the firearm cycle of operations. As used herein the terms ‘barrel extension’ refers to a component that is part of a barrel 15 assembly. A barrel extension is a part that cooperates with a bolt for locking and unlocking in the cycle of operations of a firearm described above. In additional aspects and embodiments the barrel extension provides features, including but not limited to, lugs that cooperate with features, including but not limited to lugs, on the bolt. As used herein the term ‘bolt’ refers to a component of a bolt carrier group (BCG). The bolt has 20 features, including, but not limited to lugs, that engage with corresponding features, including but not limited to lugs, on the barrel extension to allow locking and unlocking processes of the cycle of operations of a firearm described above. As used herein the term ‘primary extraction’ refers to an initial phase of the extraction process of the cycle of operations of a firearm described above, and includes an initial linear movement 25 with rotation of the bolt. Extraction is the process by which a spent cartridge is removed from the chamber of the firearm after a round has been fired. In additional aspects and embodiments ‘primary extraction’ provides an initial mechanical force suitable to overcome any resistance between the spent cartridge and walls of a firearm chamber. As used herein the term ‘barrel lugs’ refer to lugs provided on a barrel extension where a firearm 30 has a barrel extension. As used herein reference to a bolt locking describes the action of the bolt in a locking process in the cycle of operations of a firearm, the cycle including feeding, chambering, locking, firing, unlocking, extracting, ejecting, and cocking a firearm. As used herein reference to a bolt locking describes the action of the bolt in an unlocking 35 process in the cycle of operations of a firearm, the cycle including feeding, chambering, locking, firing, unlocking, extracting, ejecting, and cocking a firearm. As used herein reference to a bolt the terms ‘locked’, ‘lock’, ‘unlocked’, ‘unlock’ or similar refers to the result of the action of the bolt in a locking or unlocking process in the cycle of operations of a firearm, the cycle including feeding, chambering, locking, firing, unlocking, extracting, ejecting, and cocking a firearm. 5 As used herein the term ‘about’ in reference to rotation refers broadly to any rotation or revolution round in a circular or approximately circular course. As used herein the term ‘assembly’ refers broadly to parts that are capable of being assembled whether those parts are separated or assembled and whether those parts are able to be 10 disassembled once assembled. As used herein the term ‘axial movement’ refers broadly to movement having an axial component of movement that may also have a rotational component and the term is not limited to purely axial movement. As used herein the terms ‘axial’ in respect to movement or component of movement refers broadly to movement along an axis of the object or component 15 of the assembly that moves. As used herein the term translational movement refers broadly to movement having a translational component of movement that may also have a rotational component and the term is not limited to purely axial movement. In additional aspects and embodiments movement of a bolt actuates an extractor for the 20 extracting process of the cycle of operations of a firearm described above. Brief description of the drawings Additional and further aspects of the present invention will be apparent to the reader from the following description of embodiments, given in by way of example only, with reference to the 25 accompanying drawings in which: Figure 1 shows a bolt and barrel extension 3 assembly 1 according to a preferred embodiment of the present invention; Figure 2 shows a cutaway view of the bolt and barrel extension 3 assembly 1 of Figure 1 along plane C shown in Figure 1, with the bolt in an engaged configuration in which bolt locking lugs 30 are engaged barrel lugs; Figure 3 shows a bolt according to the embodiment of the Figures 1 and 2; Figure 4 shows an end elevation view of a barrel extension of the assembly 1 of Figures 1 to 3; and Figure 5 shows a cut-away view of the barrel extension of the barrel extension of Figure 4 along 35 the plane B shown in Figure 4; and Figure 6 shows an closer view of Figure 5; Figure 7a shows a side elevation of a bolt and barrel extension assembly according to another embodiment of the invention; Figure 7b shows a side elevation of the bolt of Figure 7a rotated about it’s axis to illustrate the pitch in the forward-facing actuation surfaces of the bolt lugs; 5 Figure 7c shows a cut-away side elevation of a barrel extension of the embodiment of Figure 7a and 7b; Figure 8 shows a close-up side elevation of a bolt of the embodiment of Figure 7a; Figure 9 shows another close-up side elevation of a bolt of the embodiment of Figure 7a; Figure 10 shows a perspective view from towards the forward end of a firearm of the bolt of the 10 embodiment of Figure 7a; Figure 11 shows a perspective view of the bot and barrel extension of the embodiment of Figure 7a from a rearward end of the firearm; and Figure 12 shows another perspective view of the bot and barrel extension of the embodiment of Figure 7a from a rearward end of the firearm. 15 Further aspects of the invention will become apparent from the following description of the invention which is given by way of example only of particular embodiments. Best modes for carrying out the invention 20 Figure 1 shows a bolt 2 and barrel extension 3 according to a preferred embodiment of the present invention. The bolt 2 and barrel extension 3 of this embodiment are separable parts that are assembled for use and are referred to herein as an assembly 1. In use, the bolt 2 is able to move relative to the barrel assembly 3 axially along a central axis C-C and also to move rotationally relative to the barrel extension 3 about the axis C-C. 25 Also shown in Figure 1 is an extractor clip 4 which engages a rim of a cartridge (not shown) to extract it from the chamber (not shown). The extractor clip 4 is connected to the bolt 2 to move with the bolt and be actuated by the bolt 2. When the bolt 2 moves rearward the extractor clip 4 moves rearward to extract the cartridge (not shown). Figure 2 gives a cut-away view of the assembly 1 along a plane in C-C of Figure 1. Figure 2 30 shows the bolt 2 received in a barrel extension 3 in a locked, engaged or closed configuration in which a chamber of a firearm is locked to fire a round (not shown). The bolt 2 may be described as locked also. The bolt 2 as shown in Figure 2 has been locked by, initially, moving axially along a central axis (C-C) of the bolt 2 and barrel extension 3 with the bolt 2 at an orientation about the central axis 35 that arranges bolt 2 locking lugs 10 to align with spaces (shown in Figure 4) between barrel locking lugs 11. This alignment with spaces between bolt extension lugs allows axial movement of the bolt 2 and bolt lugs 10 unimpeded by the barrel extension lugs 11. This allows the bolt 2 to be moved to a forward position. The bolt 2 as shown was subsequently rotated to lock the bolt 2. This is by moving the bolt lugs 10 about the central axis of the bolt C-C and into alignment about the axis of the bolt 2 with barrel lugs 11. This allows bolt lugs 10 to engage with 5 respective barrel lugs 11 to lock the bolt 2. The bolt is locked with rotation of the bolt in a first sense, or direction of rotation. Each bolt lug exemplified by 10d provides a rearward-facing surface exemplified by 20d. The rearward-facing surfaces of the bolt lugs 10 cooperate with forward-facing surfaces on barrel lugs 11 to lock the bolt in place in the barrel extension 3 and to resist recoil of a round being fired. In alternative embodiments only one of each pair of bolt 10 lugs exemplified by 10c and 10d provide a rearward-facing surface used in locking the bolt. The assembly 1 can be unlocked or disengaged by the bolt 2 being rotated in a second sense about the central axis to take the bolt lugs 10 sufficiently out of alignment with the barrel lugs 11. This will allow the bolt 2 to move axially and rearwardly to extract the cartridge and towards ejecting the cartridge and cocking the bolt. This rotation to move lugs out of alignment releases 15 or unlocks the bolt from the barrel extension. The bolt 2 is released with rotation of the bolt through a defined range of angles, in a second sense. The range of angles are determined by the geometry of the lugs and, specifically, by the width of the lugs of the bolt and barrel extension as measured about the circumference of the bolt. In this embodiment the defined range of angles is 22.5 degrees. 20 The released bolt 2 is free to move unimpeded by the barrel extension lugs 11. In this movement bolt lugs 10 pass through spaces between the barrel lugs 11. This may be forward movement or rearward movement. Rearward movement allows the bolt 2 to move rearward to remove the bolt 2 from the bolt extension 3. This may extract a cartridge. Forward movement may load a cartridge and move the bolt lugs forward ready to be rotated to lock the cartridge. 25 Figure 2 shows a bore 5 to receive a cam pin (not shown) which applies a torque to the bolt to rotate the bolt to lock it or unlock it as understood by the reader. In more detail, Figure 2 shows pairs of bolt lugs 10a, 10b engaged with pairs of barrel lugs 11a, 11b to lock the bolt 2 in the barrel extension 3. A pair of bolt lugs exemplified by 10a and 10b define a recess 12a in which barrel extension lug 30 exemplified by 11a is received. Similarly bolt lugs 10 c and 10d received define a recess 12b for barrel extension lug 11a. The set of bolt lugs 10, of which 10a to 10d are shown in Figure 2, define a groove that extends in a helix with a central axis aligned with the central axis (C-C) of the bolt to guide the bolt 2 in a helical path as the bolt is rotated about it’s central axis towards an unlocked configuration with respect to the barrel extension. The grove may be described as 35 a cam groove for a cam slider of a cylindrical cam mechanism. In more detail, forward facing surfaces of the bolt lugs, such as 10b, are able to bear against rearward facing surfaces of barrel extension lugs, such as 11a. If the bolt is rotated in an appropriate sense the forward-facing surfaces of the bolt lugs 10a bear against and slide over rearward facing surfaces of the barrel extension lugs 11a to cause the bolt to be actuated rearwardly. In the embodiment shown the groove is arranged so that the bolt is actuated rearward as the bolt is rotated in the second sense towards an unlocked orientation with respect to the barrel extension. The geometry of the helix defines a mechanical advantage of the axial, rearward component of movement of the bolt 2 to a rotational component of movement of the 5 bolt 2 in the second sense of rotation. This is towards unlocking the bolt. Figure 3 shows a plan view of the bolt 2. Bolt lugs 10 are shown arranged to be spaced at intervals around the external circumference of the bolt 2, or about the central axis of the bolt 2. Bolt lugs 10 are shown arranged in pairs, such as 10a and 10b in Figure 2 or 10a’ and 10b’ shown in Figure 3. Lugs in a pair are aligned with each other at locations around the 10 circumference of the bolt. In the embodiment of Figure 3 each pair of bolt lugs, such as 10a’ and 10b’, provides a first rearward-facing surface 20b at a rearward end of the lug and a second rearward-facing surface 20a defining a forward end of the cam groove 12. As shown in Figure 3 the groove 12 has one face, such as 21a, square (perpendicular to the central axis of the bolt) and the opposing face 15 20a angled (angled with respect to the to the central axis of the bolt). In this embodiment a forward-facing surface 21a in the groove 12, provided by the rearward lug 10b’ of a pair of aligned lugs has the same pitch angle as locking surfaces 20a and 20b of the bolt lugs. Each bolt lug 10 of this embodiment also provides a forward-facing surface 21a and 21d. A 20 forward-facing surface faces approximately towards the front of the firearm. The forward-facing surfaces 21 of bolt lugs 10, of this embodiment, are not precisely forward-facing because they conform to a helix. In this embodiment lugs 10 are arranged in pairs arranged about the periphery of the bolt about the central axis. Forward lugs 10a and rear lug 10b make up a pair. 25 In this embodiment a first forward-facing surface 21b is provided by a first, forward lug 10a of a pair of lugs 10. In this embodiment also, a second forward-facing surface 21a is provided by a second lug 10b of the pair. In some embodiments the cam groove 12 is formed during fabrication into a lug blank that resembles a single, elongate bolt lug extending parallel to the central axis of the bolt. The lug blank with cam groove 12 defines two lugs 10a and 10b from a 30 single elongate lug blank. The bolt lugs 10 of this embodiment provide second forward-facing surfaces 21a which conform to a helix (not shown) common to the second forward-facing surfaces 21 of all bolt lugs 10. The bolt lugs 10 of this embodiment provide first forward-facing surfaces 21b which conform to a helix (not shown). Second forward-facing surfaces 21b’ are shown also. 35 These first forward-facing surfaces 21a of the bolt lugs 10a may be referred to as actuation surfaces of the bolt lugs 10a. These might be alternatively described as defining a helix. Each helix has a central axis oriented along the central axis of the bolt. Figures 4 to 6 show a barrel extension 3 of the same embodiment of the invention as Figures 1 to 3. Figures 4 shows an end-on elevation view of the barrel extension 3. Figures 5 and 6 show 5 cross-section along B-B of Figure 4. Barrel locking lugs 11 are arranged spaced at intervals around an internal circumference of the barrel extension 3. The circumference is shown in the plane perpendicular to the page in Figure 5. The barrel locking lugs 11 shown in Figure 5 have rearward-facing surfaces 22 provided to cooperate with forward-facing surfaces 21a on bolt lugs 10 to actuate the bolt along it’s axis. 10 Primary extraction for the firearm is provided by the bolt lugs 10 being guided to rotate and move axially as defined by the helix. A dashed line is shown parallel to the rearward facing surfaces 22 of the barrel locking lugs. A dotted line 23 is shown perpendicular to the central axis of the barrel extension. An angle ǿ 24 shown between the lines parallel to the rearward-facing barrel lug surfaces and the line 15 perpendicular to the central axis. This angle a depicts a pitch of the helix that the rearward- facing surfaces 22 of the barrel extension lugs conform to. These rearward-facing surfaces on the barrel locking lugs cooperate with corresponding forward-facing surfaces 21a on bolt lugs 10a by shearing over the forward-facing surfaces of the bolt lugs. This causes the bolt lugs to move along the helix as the bolt is rotated. The pitch of the helix defines an axial component of 20 movement of the bolt as the bolt lugs follow the helix. The forward-facing surfaces of the bolt lugs and cooperating rearward-facing surfaces of the barrel locking lugs thereby convert a rotational torque to an axial force component to actuate the bolt rearwards. These surfaces may be referred to as actuation surfaces. The actuation surfaces actuate the bolt axially with rotation of the bolt as defined by the helix, or the pitch of the helix. The reader will appreciate that a pitch 25 of, say, 5 to 10 degrees will provide significant mechanical advantage to the axial component of movement of the bolt due to a torque which rotates the bolt about it’s central axis. In this embodiment rotation by 22.5 degrees is required to move the bolt lugs from alignment with barrel lugs in a locked configuration to alignment with spaces between barrel lugs 25 in an unlocked configuration. In this embodiment the helix that the lug surfaces conform to is 30 designed in the range of 5 to 10 degrees. The rearward-facing surfaces of barrel lugs 11 are shown at an angle away from perpendicular to the central axis. In this example the rearward-facing surfaces 22 are shown at an angle to the central axis to depict a pitch of aa helix. This is, the rearward surface of the barrel lugs will lie on, or conform to, a helical surface defined in the space of the barrel extension with a central 35 axis of the helix lying along a central axis of the barrel extension 3. The barrel locking lugs 11 as shown in Figure 4 may be considered as cut in a helical configuration. The barrel lugs 11 of this embodiment provide spaces 25 therebetween to admit bolt lugs 10, as shown in Figure 4, when the bolt 2 moves forward into the barrel extension 3 or rearward out of the barrel extension 3. These spaces 25 extend parallel to the central axis of the barrel extension to allow the bolt to move axially when the bolt is oriented with the bolt lugs 10 aligned with these spaces. The spaces 25 allow the firearm to load a cartridge before the bolt is locked and allow secondary extraction of the cartridge after the bolt is unlocked. The barrel lugs 11 and bolt lugs 10 are dimensioned so that rotation of the bolt 2 in a first sense 5 through a defined range of angles will disengage the bolt 2 locking lugs from the barrel locking lugs to allow the bolt 2 to move rearwards with respect the firearm. In this rearward movement the bolt 2 locking lugs pass through the spaces 25 defined by an angle provided between the barrel locking lugs. This will allow a cartridge to be extracted. Rearward-facing surfaces (not shown) of the bolt lugs 10 and forward-facing surfaces 23a and 10 23 b of the barrel lugs cooperate to lock the bolt in the barrel extension when the bolt is rotated in a first, locking sense. The rearward-facing surfaces of the bolt lugs and cooperating forward- facing surfaces of the barrel lugs may be referred to herein as locking surfaces. When the bolt is rotated in a second, unlocking sense forward-facing surfaces on the bolt lugs 10 and rear-facing surfaces on the barrel lugs 11 cooperate to actuate the bolt 2 rearward as 15 defined by the pitch of the helix. In this embodiment cooperating surfaces slidingly bear on each other, and shear relative to one another, to cause the bolt to move with a component of movement being rotational about the axis C-C of the bolt and a component of movement being along the axis C-C of the bolt. This movement of the bolt may be described as rotating and translating as defined by the helix. This movement of the bolt may be described as having a 20 rotational component and translational component as defined by the helix. Specifically in this embodiment the actuation of movement is a component of movement along the axis defined by the pitch of the helix. The helix defines a rate of movement along the axis of the bolt 2 for rotation of the bolt. Cooperating surfaces of the barrel lugs 11 and bolt lugs 10 are arranged to cooperate so that rotation of the bolt 2 in a sense towards the lugs disengaging 25 actuates the bolt 2 with a component of movement along the central axis of the bolt. Specifically, the helix conforming surfaces are arranged to cooperate to actuate the bolt 2 with a component of movement towards the rear of the firearm. Barrel locking lugs are formed by machining, in this preferred embodiment, on the barrel extension. 30 Bolt 2 locking lugs are formed on the bolt, in this embodiment, by machining. The barrel locking lugs 11 and bolt locking lugs 10 arranged to engage when the bolt 2 is rotated about a central axis of the bolt 2 in a first sense to lock the bolt 2 in the barrel extension. The lugs 11 and bolt lugs 10 are arranged to disengage by rotation of the bolt 2 about said axis in a second, opposite sense. Engagement is arranged by the dimensions and shape of the lugs 35 and their location on respective barrel extension 3 or bolt. In this embodiment engagement moves engagement surfaces of the lugs that are oriented approximately perpendicular, or transverse to a central axis of the bolt 2 to overlap and be in contact to lock the bolt 2 in the barrel extension. These surfaces, which engage to lock the bolt 2 and barrel extension 3, may be referred to herein as locking surfaces. The lugs which provide the locking surfaces may be referred to as locking lugs. When in contact, engaged, the locking surfaces resist rearward a recoil impulse on the bolt 2 caused by a round in the firearm being fired. In this embodiment the locking surfaces provided 5 by the barrel extension 3 lugs face forwards with respect to the firearm. In this embodiment the locking surfaces provided by the bolt 2 lugs face rearwards with respect to the firearm. In this embodiment the barrel locking lugs and bolt 2 locking lugs are arranged by shape, dimension and location on respective parts to disengage from each other as the bolt 2 is rotated about it’s central axis in a second, disengagement sense sufficiently to take the barrel lugs and 10 bolt lugs out of alignment around the circumference of the barrel extension. The barrel extension 3 locking lugs and bolt 2 locking lugs are arranged by shape, dimension and location to that the barrel locking lugs provide a range of angles, or spaces around the internal circumference of the barrel extension 3 for the disengaged bolt 2 lugs to pass through as it moves towards the rear of the firearm. In this particular embodiment 22.5 degrees of 15 rotation is required to lock or unlock the bolt. This is to rotate the bolt locking lugs 10 from full alignment with the barrel lugs 11 to full alignment with spaces 25 between the locking lugs 11. Disengagement of the lugs allow the bolt 2 to move along an axis of the bolt 2 to remove the bolt 2 from the barrel extension, characterised in that the bolt 2 locking lugs and barrel locking lugs have actuation surfaces arranged to cooperate to actuate the bolt 2 with a component of 20 movement along said axis as the bolt 2 is rotated to disengage the barrel locking lugs and bolt 2 lugs. In this preferred embodiment the locking surfaces of the barrel extension 3 and bolt 2 are arranged by shape, dimension and location on respective parts of the assembly 1 to disconnect from each other after a small degree of rotation. This may be referred to as disconnecting 25 immediately. This disconnection allows space between opposing locking surfaces for rearward actuation of the bolt 2. This actuation is provided by the helix-conforming actuation surfaces provided on the barrel lugs 11 and cooperating surfaces on the bolt lugs 10. This cooperating and actuation may be recognised as the cooperating actuation surfaces each conforming to a helix in common moving over each other to actuate the bolt 2 relative to the bolt. In this example 30 this actuation is movement of the bolt 2 towards being out of and away from the barrel extension. In this embodiment the movement is defined relative to rotation of the bolt. This may be considered as defined by the pitch of the helix. In this embodiment each barrel lug and each bolt 2 lugs provides two actuation surfaces. The actuation surfaces may be referred to as providing a dual helix configuration of actuation surfaces. 35 Figure 4 shows a space 26 about the internal circumference of the barrel extension for an extraction clip which has a tool to engage a rim of a cartridge of a round to extract the round. The extraction clips is fixed relative to the bolt 2 to that it pulls the rim of a cartridge as the bolt 2 is actuated rearwardly. The operation of the assembly 1 will now be illustrated. When oriented at a first angle about its central axis locking lugs on the bolt 2 align rotationally about a central axis with spaces 25 or empty angular regions defined between locking lugs 11 on the barrel extension 3. This allows the bolt 2 to be moved axially and forward so the bolt 2 5 enters the barrel extension 3 as bolt 2 locking lugs moving past barrel locking lugs. When the bolt 2 is at a forward position in the barrel extension 3 the bolt is rotated to align the bolt lugs 10 with barrel lugs 11. The bolt is rotated in a first sense to engage rearward surfaces of the bolt lugs with forward surfaces of the barrel lugs to lock the bolt for firing. When aligned rearward-facing, locking surfaces provided by the bolt 2 locking lugs 10 are forward and beyond 10 forward-facing locking surfaces provided by the barrel locking lugs 11. They may be beyond by a designed tolerance. After firing, or to remove an un-fired cartridge, the bolt 2 is rotated in a second unlocking sense sense. This rotation causes forward-facing actuation surfaces on bolt lugs 10 engage with rearward-facing actuation surfaces on the barrel lugs 11. These rearward and forward-facing 15 surfaces cooperate by sliding over each other to move the bolt lugs along a helix until the bolt lugs are sufficiently rotated to be clear of the barrel lugs. This helical movement of the bolt lugs, relative to the barrel lugs, has a component of rotation and a component of movement along the axis of the bolt. In this embodiment the movement along the axis is rearward. This axial movement is defined by the shape of the helix. In additional embodiments the component of 20 rearward movement in the axis of the bolt is defined to provide mechanical advantage to remove a cartridge from the chamber. The component of rearward movement actuated by the shape of the helix, which is defined as optimal for primary extraction of a cartridge. In preferred embodiments 22.5 degrees of rotation is required to unlock the bolt and the helix has a pitch of 5 to 10 degrees. 25 Aspects of manufacture of a bolt according to the preferred embodiment will now be described. During the fabrication of a bolt, blanks for lugs are formed on an outside periphery of the bolt. The bolt is elongate with a central axis and has a periphery arranged perpendicular to the axis. This periphery may be represented by the periphery of a cross-section cut perpendicular to the central axis. It is tis periphery which will have lugs formed thereon to engage with lugs of a 30 barrel extension. The lug blanks provide an elongate raised portion of the circumference of the bolt aligned parallel with a central axis of the bolt. A groove is formed in the lug blank. The groove may be a groove for a cam, or a cam groove. The groove extends transverse to the elongate lug blank to separate the lug blank into two lugs or lug sections. A face of the groove that will face forward with respect to a firearm when the bolt is in use has a forward-facing 35 surface. The groove also has a rearward-facing surface formed on it. This rearward-facing surface is formed to engage with a cooperating forward-facing surface of a bolt extension to lock the bolt. During fabrication of a barrel extension lugs which are located in use over an extractor are omitted for fabrication. The space 26 provided by these omitted lugs receive part of a machining tool that forms barrel lugs. This provides advantages for forming barrel lugs with surfaces that conform to a helix. Figure 7a shows a side elevation of disassembled bolt 32 and a barrel extension assembly 30 according to another embodiment of the invention. In these embodiments actuation surfaces 31 5 on the bolt 32 are provided by an elongate lug 33 with a groove 34 formed therein. A set of lugs 33 is arranged about the external periphery of the bolt. In this embodiment each groove 34 is located approximately at the same position along the central axis of the bolt. This is illustrated by the forward-facing surfaces 31 surfaces, defined by the groove 34, at approximately the same distance 36 from a rearward-facing edge 35 of the lug 33. 10 Figure 8 shows a closeup of the bolt of Figure 7a. As shown in Figure 8, a forward-facing surface 31 formed on the bolt 32 is approximately perpendicular to the central axis of the bolt in a first dimension. This is the central axis of the bolt as shown lies in the plane of the page and the surface 31 extends directly out of the page in a first dimension, represented at a normal to the page or directly out of the page. The surface 31 is also angled with respect to the central 15 axis by the angle 37. If line 38 represents a plane perpendicular to the central axis of the bolt in two dimensions then surface 31 is perpendicular in the first dimension, similarly to plane 38, and also at angle 37 to the central axis in a second dimension. The angle of the surface 31 in the second dimension is shown by line 39. The reader will understand the surface as a 3- dimensional surface, with the central axis of the bolt aligned with a third dimension. 20 Because of the angle 37 a cross-section 40 of the bolt 39, represented as out of the page and parallel to the central axis of the bolt across the page, will be progressively forward as the bolt is rotated towards unlocking the bolt. As shown this would appear as rotation in a sense represented by arrow 29. The line 40 ‘ represents the cross-section 40 with the barrel rotated but the view adjusted for the orientation of the bolt. By the action of the cross-section moving 25 forward the cross-section of surface 31 would be forced against a cooperating surface 41 of the barrel-extension lugs and would force the bolt 32 rearward relative to the barrel extension. By the selected angle 37 a degree of rearward movement would be provided by a degree of rotation towards unlocking the bolt. The reader will appreciate that the moving bolt moving as described here has a component of rotational movement and a component of axial movement. 30 The axial movement is defined by the angle 37. The angle 37 of the actuation surface 31 can be arranged so that rotation through a range of angles required to take the bolt from locked to unlocked causes the bolt to move rearwardly by a distance or mechanical advantage suited to primary extraction by an extractor (not shown) coupled to the bolt. In the embodiment shown in Figure 8 the angle required to move the bolt 35 from being locked, in a locked configuration, and unlocked, in an unlocked configuration, is approximately 22 degrees. Figure 7b shows the bolt of Figure 7a displayed as rotated to illustrate the pitch on the forward-facing surfaces of the bolt lugs 33. As shown the forward- facing surface 31g is offset along the bolt by a distance 50. In this embodiment rear-facing surfaces 51 of the bolt lugs follow the same pitch as the forward-facing surfaces 31. Figure 7c shows a cross-section of the barrel extension 30. Shown in Figure 7a are barrel lugs 61 defining helical conforming rearward-facing actuation surfaces 52. Also shown are forward- facing locking surfaces 63. Figure 10 shows a perspective view from the front of the bolt 32 of Figure 9. A groove 34 is 5 shown formed in lugs 33. Figure 11 shows a perspective view from the rear of a barrel extension 47 of the embodiment of Figure 10. As shown the barrel extension has a set of barrel lugs, or barrel extension lugs 42 arranged around the internal circumference of the barrel extension. Forward barrel extension lugs 43 provide a rearward facing surface 41 which cooperates with forward facing actuation 10 surfaces 31 of the bolt lugs 33. Rearward barrel extension lugs 44 provide forward-facing surfaces 45 which cooperate with rearward facing surfaces 46 of bolt lugs 33 to brace the bolt against recoil. As shown in Figures 7 to 12 bolt lugs 33 each define a groove 34 into which forward barrel extension lugs 43 are received as the bolt is rotated relating to the barrel extension to lock the 15 bolt. In this particular embodiment the groove 34 is angled and the forward barrel extension lugs 43 are shaped so the groove 34 defines movement of the bolt relative to the barrel extension to move the bolt along the rearward as it is rotated towards unlocking. From the point of view of the bolt, the forward lugs 43 move along the groove 34 as the bolt moves relative to the barrel extension. 20 In the embodiment of Figure 7 the rear-facing surfaces on the bolt, which the reader will understand provided bracing or resistance against recoil, also conform to the same helix shape. This means that when a torque is applied to rotate the bolt to lock the bolt the rear-facing surfaces will bear cooperating forward facing surfaces on bolt lugs, or otherwise provided by the barrel extension. By the action of helical rear-facing surfaces of the bolt lugs and cooperating 25 helical forward-facing surface on barrel lugs the torque towards locking the bolt actuates the bolt with an axial and axially forward component. The reader will appreciate the helical rear-facing surfaces of the bolt lugs and cooperating helical forward-facing surface on barrel lugs will slide over each other leaving little or no space. This will obviate grit or contaminants accumulating between the surfaces. The reader will appreciate the helical rear-facing surfaces of the bolt lugs 30 and cooperating helical forward-facing surface on barrel lugs will preload or prestress the bolt lugs. The reader will appreciate the helical rear-facing surfaces of the bolt lugs and cooperating helical forward-facing surface on barrel lugs will minimise or eliminate tilting of the bolt. This is particularly where preloading occurs. The reader will appreciate the helical rear-facing surfaces of the bolt lugs and cooperating helical forward-facing surface on barrel lugs will spread recoil 35 load evenly over the bolt lugs. Further and additional embodiments will now be described. In an alternative embodiment to that shown in Figure 7 the surfaces described with reference to a bolt lug may be provided by a barrel lug. In this embodiment the surfaces described with reference to a barrel lug, or barrel extension lug, lug may be provided by a bolt lug. For example the cam groove may be formed in the barrel lugs and bolt lugs may be dimensioned to move along the cam groove as cam sliders. The barrel extension and bolt of additional embodiments are separable parts that are assembled for use and may be referred to as an assembly. 5 In alternative embodiments a bolt lug provides a single forward-facing surface. In other embodiments each bolt 2 locking lug provides three or more forward-facing surfaces. In alternative embodiments a bolt lug provides a single rearward-facing surface. In other embodiments each bolt lug provides three or more rearward-facing surfaces. The term ‘sense’ of rotation may be recognised by the reader as the technical term for direction 10 of rotation. For example, clockwise may be one sense and anticlockwise may be the opposite sense. In additional embodiments actuation surfaces of lugs conform to a helix. In additional embodiments the helix is a three-dimensional (3-D) curve that lies on a cylinder, so that its angle to a plane perpendicular to theaxis is constant. 15 In other embodiments the actuation surfaces have alternative three-dimensional surface shapes known to the reader as suitable to actuate the bolt 2 rearwardly as the bolt 2 is rotates towards disengagement of barrel locking lugs and bolt 2 locking lugs where these alternatives are known to the reader to be suitable for given applications and / or manufacturing processes. In one alternative embodiment the actuation surfaces are planar set at angles to the central axis of the 20 bolt 2 to cause rearward actuation of the bolt 2 as it is rotated. In another alternative embodiment the actuation surfaces are each provided by one or more cams set in one or more of the barrel locking lugs and bolt 2 locking lugs. In another alternative embodiment the actuation surfaces are each provided by one or more gears set in one or more of the barrel locking lugs and bolt 2 locking lugs. The gears may be mounted eccentrically. 25 In additional embodiments the pitch of a helix to which actuation surfaces conform is selected to be in the range of 5 to 10 degrees. In some embodiments the bolt lugs are formed to follow a helix. In other embodiments actuation surfaces of the lugs are formed to conform to a helix. In other embodiments actuation surfaces and locking surfaces are formed to conform to a helix. 30 Additional embodiments have the following alternative configurations of surfaces provided by the groove formed in a lug blank: i. one face square, second angled 15-45 degrees, no order ii. both faces square, and iii. both faces angled 15-45 degrees. In additional embodiments an actuation surface conforming to a surface means that a number of actuation surfaces will coincide with a surface defining the helix common to the number of actuation surfaces. In alternative embodiments alternatives to machining known to the reader as suitable for given 5 applications or manufacturing processes are used to form lugs and / or the barrel extension 3 or bolt. Examples include but are not limited to forging, casting, laser cutting and 3-D printing. In additional embodiments any know method of machining is used to form lugs and / or the barrel extension 3 or bolt. Various examples include but are not limited to CNC milling, polishing, grinding. 10 In additional embodiments movement along an axis or parallel to an axis is translation. In additional alternative embodiments or alternative aspects, a barrel extension 3 may be substituted with a barrel. In additional alternative embodiments or alternative aspects a barrel extension 3 may be substituted with a section of a barrel. In additional alternative embodiments or alternative aspects, a barrel extension 3 may be 15 substituted with a chamber. In additional alternative embodiments or alternative aspects a barrel extension 3 may be substituted with a section of a chamber. In additional embodiments and aspects of the invention degrees of rotation may be substituted for radians of rotation by equivalents known by the reader. The reader may recognise the bolt 2 and the barrel extension 3 as components of a firearm. 20 The bolt 2 and barrel extension 3 may be recognised as an assembly 1 of components. The bolt 2 and barrel extension 3 may be recognised as an assembly 1 of components. In additional embodiments the barrel and bolt 2 extension may be recognised as an assembly 1 even in a state disassembled from each other. In additional embodiments a secondary groove on bolt 2 lugs increases bearing shear surfaces 25 of each bolt 2 lugs. In some embodiments this may be an increase of 25%. In additional embodiments the bearing shear surfaces are actuation surfaces. Additional embodiments of the invention provide an advantage of a smoother gas operated firearm. In some embodiments this advantage is particularly enjoyed at lower cycle rates. 30 In some embodiments this advantage is particularly enjoyed at suppressed cycle rates. Embodiments of the invention provide an advantage of a smoother manually operated firearm. Various embodiments of the invention an advantage relating to unbalanced bolt 2 lugs. In a conventional AR platform bolt, or similar, debris between bolt 2 and barrel lugs on a side of the bolt 2 opposite the extractor may cause the bolt 2 to tilt and cause extra load on two lugs either side of the extractor, The reader may recognise these as the two weakest lugs on the bolt. Lugs with helical surfaces of additional embodiments of the present invention cause any debris to take a path of least resistance which does not result in debris between the bolt 2 lugs and 5 barrel lugs and does not result in tilt of the bolt. Lugs with helical surfaces of additional embodiments of the present invention cause any debris to scrape debris away preventing debris remaining on the lugs which may otherwise cause tilt of the bolt. Lugs with helical surfaces of additional embodiments of the present invention allow a tolerance 10 between bearing surfaces of the barrel lugs and bolt 2 lugs that do not allow debris between these bearing surfaces which may otherwise cause tilting of the bolt. Sets of bolt lugs and cooperating barrel lugs in additional embodiments illustrated herein allow the bolt to thread into the barrel extension. For example, the bolt may be threaded to unlock the bolt by lugs with helical actuation surfaces described defining a threading movement. 15 In additional embodiments leading and trailing surfaces of the bolt 2 lugs and barrel extension 3 lugs allow the bolt 2 to translate in a 2-D plane, as tolerances allow, but do not allow 3-D tilting. In additional embodiments a redundant lug on the barrel extension 3 where the extractor resides is omitted to allow access for a tool to machine the barrel extension 3 lugs. Embodiments of the invention provide actuation surfaces that utilise rotation of the bolt 20 performed in an unlocking process to provide mechanical advantage in an axial direction to provide primary extraction. Embodiments of the invention provide locking lugs in a helical configuration to utilise rotation of the bolt performed in an unlocking process to provide mechanical advantage in an axial direction to provide primary extraction. 25 Embodiments of the invention provide locking lugs in a helical configuration to utilise rotation of the bolt performed in an unlocking process to provide mechanical advantage in an axial direction to provide primary extraction. Embodiments of the invention provide actuation surfaces that utilise rotation of the bolt performed in an unlocking process performed in a gas-operated firearm to provide axial 30 mechanical actuation of the bolt and associated extractor primary extraction where the rate of axial actuation is lower than otherwise provided by a gas-operated bolt. Embodiments of the invention provide actuation surfaces that utilise rotation of the bolt performed in an unlocking process performed in a gas-operated firearm to provide axial mechanical actuation of the bolt and associated extractor primary extraction where the force of 35 actuation is lower than otherwise provided by a gas-operated bolt. In alternative embodiments actuation surfaces arranged to actuate the bolt along a central axis of the bolt may be provided other than on forward-facing faces of the bolt lugs. In alternative embodiments actuation surfaces arranged to actuate the bolt along a central axis of the bolt may be provided other than on rearward-facing surfaces of barrel lugs. 5 In some of these alternative embodiments the bolt lugs may have actuation surfaces formed on a peripheral face of the lug. In additional of these embodiments the actuation surfaces formed on a periphery may be a thread. The reader will recognise that a bolt which has lugs moving along a helix will have a component of movement that is rotational about a central axis of the bolt and a component of movement 10 that is axial and that these ‘components’ can be added to describe the movement of the bolt. Additional aspects and embodiments are illustrated here with the terms ‘helix’ is substituted with ‘spiral’. In the embodiments of Figures 1 to 6 and / or the embodiment of Figures 7 to 9, the bolt and barrel extension assembly may be in a locked configuration when the bot is locked and in an 15 unlocked configuration when the bolt is unlocked ready to move rearwardly with bolt lugs moving in spaces between barrel extension lugs. In alternative embodiments to those of Figure 1 or Figure 7a each bolt lug in a set of lugs may have surfaces similar to surface 31 which conforms to a helix of the same pitch as helix’s of other lugs but rotated about the central axis of the bolt relative to helix’s of other lugs. 20 In alternative embodiments of Figure 1 or Figure 7a each bolt lug may have surfaces similar to surface 31 which conforms to a helix of the same pitch as helix’s of other lugs but rotated about the central axis of the bolt relative to helix’s of other lugs in a set of lugs arranged about the periphery of the lugs. The forward-facing surface might be described as conforming to a section of a helix. The forward-facing surface might be described as conforming to a truncated helix. 25 In alternative embodiments of Figure 1 or Figure 7a each bolt lug may have surfaces, exemplified in Figure 7a by surface 3, may conform to a plane. In alternative embodiments of Figure 1 or Figure 7a each bolt lug may have surfaces, exemplified in Figure 7a by surface 3, may provide a thread. The surface, exemplified by 31, may conform to a section of a thread or a truncated thread. 30 In a further embodiment a cam groove similar to 34 defined by bolt lugs and barrel-extension lugs similar to 33 provide a cylindrical cam mechanism. The reader will appreciate that the groove 34 is arranged over a cylindrical surface and the lugs 33 move along the cam groove. This is even if the cam groove is formed through a single bolt lug, whether cam grooves through different bolt lugs are staggered along the length of the bolt, or whether a cam groove extends 35 through the set of bolt lugs. In additional embodiments the bolt lugs convert a torque applied to the bolt, or rotational movement caused by, by a cam pin to the cam pin bore. The bolt moves in a in a first mode of movement which is rotational and axial when bolt lugs overlap, are in overlapping alignment with, barrel-extension lugs. The bolt moves in a second mode with bolt lugs aligned with spaces 5 arranged radially inward from the barrel extension and defined between adjacent barrel- extension lugs. In the first mode the angle of the groove, such as 34, the forward-facing surfaces of the bolt lugs or rearward-facing surfaces of the barrel-extension lugs the angle being with respect to a plane that is perpendicular to the axis of the bolt defines a mechanical advantage of a torque applied by a cam pin to axial movement of the bolt. This plane 10 perpendicular may be recognised as the cross-section of the bolt. The torque applied to the cam pin bore, such as 5, acts to unlock the bolt by rotating it towards the bolt lugs being aligned with spaces between barrel-extension lugs. The torque may be referred to as an unlocking torque. In the second mode of movement the bolt lugs are aligned with spaces between the barrel- extension lugs and moves under actuation of a piston, well known to the reader, driven by 15 gases from propellant associated with a cartridge. In additional embodiment, such as that shown in Figure 1, the second mode is purely axial with rotational orientation of the bolt relative to the barrel extension being guided by the barrel-extension lugs to stay in the spaces therebetween. The second mode serves as secondary extraction of the cartridge. Additional aspects and embodiments are illustrated here with the terms ‘helix’ is substituted with 20 corkscrew. Further aspects and embodiments are illustrated here with corkscrew and spiral being examples of helix. In further aspects and embodiments lugs on a bolt are arranged to act a thread for the bolt. In alternative embodiments each pair of bolt lugs provides only one forward facing surface that 25 bears on a barrel lug to actuate the bolt rearward, referred to here as an actuation surface. In additional of these embodiments the actuation surfaces are provided on a surface provided by a rear lug in a pair. In alternative embodiments each bolt lugs with groove formed therein provides only one forward facing surface that bears on a barrel lug to actuate the bolt rearward, referred to here as an 30 actuation surface. In additional of these embodiments the actuation surfaces are provided on a surface provided by the groove. In a further embodiment the bolt has pairs of lugs with each lug providing a first forward surface forward-facing surface that conforms to a helix having a central axis in common with a central axis of the bolt and a second forward facing surface that conforms to a plane which is 35 perpendicular to the central axis. In alterative further embodiments the bolt has lugs which each provide a first forward surface forward-facing surface that conforms to a helix having a central axis in common with a central axis of the bolt and a second forward facing surface that conforms to a plane which is perpendicular to the central axis. In a further embodiment the bolt has a set of pairs of forward lugs and rearward lugs wherein the set of one of the forward or rearward of the pairs are arranged in a helix. 5 In a further embodiment the bolt has a set of pairs of forward lugs and rearward lugs wherein the set of one of the rearward lugs are arranged in a helix. In some embodiments a locking surface may be located opposite and distal to an actuation surface on a respective locking lug on a bolt and a locking surface of a barrel extension may be located oppose an actuation surface of a barrel extension on a pair of locking lugs on a barrel 10 extension. In some embodiments a locking surface may be located opposite and distal to an actuation surface on a respective locking lug of a barrel extension and a locking surface of a barrel extension may be located oppose an actuation surface of a bolt on a pair of locking lugs on a barrel extension. 15 In an alternative aspect the invention provides a bolt with elongate locking lugs extending parallel to a central axis of the bolt and comprising one or more surfaces defined by a groove transverse to the axis is formed in the elongate lug. The groove may be a cam groove. Groove formed in a set of the lugs may conform to a helix. 20 In an alternative aspect the invention provides a bolt with a set of elongate locking lugs each lug extending parallel to a central axis of the bolt and each comprising one or more surfaces defined by a groove transverse to an axis of the elongate lug that is parallel to the central axis. The groove may be a cam groove. The bolt may have a set of lugs and the groove may be formed in the set of the lugs may be helical. 25 In an alternative aspect the invention provides a bolt with a set of elongate locking lugs each lug extending parallel to a central axis of the bolt and each comprising one or more surfaces defined by a groove extending in a spiral The spiral may have a central axis in common with a central axis of the bolt. 30 In some embodiments each barrel locking lug may define two actuation surfaces. In an alternative embodiment to that shown in Figures 7, a barrel extension in integral with the barrel. For example, the barrel extension is formed from a unitary piece of metal with the barrel. In this embodiment barrel extension does not imply a separate part to the barrel. 35 In some embodiments a locking surface may be located opposite and distal to an actuation surface on a respective locking lug of a barrel extension and a locking surface may be located oppose an actuation surface of a barrel extension on cam groove formed in an elongate locking lug on a bolt. In the preceding description and the following claims the word ‘comprise’ or equivalent variations thereof is used in an inclusive sense to specify the presence of the stated feature or features. This term does not preclude the presence or addition of further features in additional embodiments. Similarly ‘a’ used in respect of a component or element does not exclude 5 ‘another’. It is to be understood that barrel lugs being provided on a barrel extension is only exemplary of firearms that have a barrel extension to illustrate the invention involving helical actuation surfaces. It is to be understood that barrel lugs being provided on a barrel extension is only exemplary of firearms that have a barrel extension to illustrate the invention involving the invention involving a bolt threading into or out of a locked configuration. In alternative types of 10 firearm that do not have barrel extensions, aspects of the invention or embodiments of the invention may substitute bolt and barrel extension assemblies and barrel extension lugs for bolt and barrel assemblies, bolt and chamber assemblies and may substitute barrel extension lugs for barrel lugs or chamber lugs. It is to be understood that the present invention is not limited to the embodiments described 15 herein and further and additional embodiments within the spirit and scope of the invention will be apparent to the skilled reader from the examples illustrated with reference to the drawings. In particular, the invention may reside in any combination of features described herein, or may reside in alternative embodiments or combinations of these features with known equivalents to given features. Modifications and variations of the example embodiments of the invention 20 discussed above will be apparent to those skilled in the art and may be made without departure of the scope of the invention as defined in the appended claims.

Claims

Claims:

1. A bolt and barrel extension assembly for a firearm having a forward end and a rear end the assembly having a set of bolt lugs arranged about the circumference of the bolt and a set of 5 barrel-extension lugs arranged about the internal circumference of the barrel extension, wherein the assembly has an unlocked configuration in which the bolt lugs are aligned with spaces defined between barrel extension lugs and in which the bolt is able to move rearwardly to extract a cartridge from the barrel extension, wherein the assembly has a locked configuration in which the bolt lugs are aligned with the barrel extension lugs, and wherein the bolt comprises a bore for a cam pin operable to provide an unlocking torque applied to the bolt to actuate the bolt towards the unlocked configuration, wherein the bolt lugs define forward-facing surfaces operable to bear against cooperating reward-facing surfaces defined by the barrel-extension lugs to convert the unlocking torque to an axial component of force on the bolt towards the rear of the firearm.

2. The bolt and barrel extension assembly of claim 1 wherein primary extraction of a cartridge is actuated by the axial component of force provided by the forward-facing surfaces bearing against cooperating reward-facing surfaces.

3. The bolt and barrel extension assembly of claim 1 or claim 2 operable to allow secondary extraction of a cartridge by bolt lugs being aligned with spaces between barrel-extension lugs allowing the bolt to move unimpeded by the barrel extension.

4. The bolt and barrel extension assembly of any one of claims 1 to 3 wherein the forward- facing surfaces of the bolt lugs are arranged so as to bear against cooperating rear-facing surfaces of the barrel-extension lugs to cause the actuating torque to actuate the bolt to rotate and move rearwards.

5. The bolt and barrel-extension assembly of any one of claims 1 to 4 wherein the bolt lugs define forward-facing surfaces operable to bear against cooperating reward-facing surfaces defined by the barrel-extension lugs to cause the bolt lugs to move to follow a helix.

6. The bolt and barrel extension assembly of any one of claims 1 to 5 wherein the forward- surface of the bolt lugs may be arranged at an angle to a plane arranged perpendicular to an axis of the bolt.

7. The bolt and barrel extension assembly of any one of claims 1 to 6, wherein the cooperating rear-facing surfaces on the barrel extension lugs may be arranged at a cooperating angle to a plane arranged perpendicular to an axis of the barrel extension.

8. The bolt and barrel extension assembly of claim 6 or claim 7 wherein said angle and cooperating angle may be arranged such that movement of the bolt under the unlocking torque through a range of movement required to unlock the bolt applies the axial force suitable for primary extraction of a cartridge over an axial distance suitable for primary extraction.

9. The bolt and barrel extension assembly of any one of claims 1 to 8 wherein the forward- facing surface of the bolt lugs and cooperating rear-facing surfaces on the barrel extension lugs may be arranged to cooperate by slidingly bearing against each other.

10. The bolt and barrel extension assembly of any one of claims 1 to 9 wherein the set of bolt 5 lugs define forward-facing surfaces on the bolt lugs with a cam groove formed in the set of bolt lugs.

11. The bolt and barrel extension assembly of claim 10 wherein the set of barrel extension lugs are dimensioned to be able to move along the cam groove.

12. The bolt and barrel extension assembly of claim 10 or claim 11 wherein the set of barrel extension lugs provide cam pins which move along the cam groove.

13. The bolt and barrel extension assembly of any one of claims 10 to 12 wherein the cam groove may be arranged as a helix.

14. The bolt and barrel extension assembly of any one of claims 10 to 13 wherein the set of barrel-extension lugs may comprise portions arranged so as to be operable to be received in the cam groove such that movement of the bolt lugs is defined by the helix of the cam groove.

15. The bolt and barrel extension assembly of any one of claims 1 to 9 wherein the set of barrel extension lugs define rear-facing surfaces with a cam groove formed in the set of barrel extension lugs.

16. The bolt and barrel extension of claim 15 wherein the set of bolt lugs are dimensioned to move along the cam groove formed in the set of barrel extension lugs.

17. The bolt and barrel extension assembly of any one of claims 10 to 16 wherein a cam groove may be arranged as a helix.

18. The bolt and barrel extension assembly of claim 15 wherein the set of bolt lugs may comprise portions arranged so as to be operable to be received in the cam groove such that movement of the bolt lugs under a torque towards unlocking the bolt is defined by the helix of the cam groove.

19. The bolt and barrel extension assembly of claim 4 wherein the angle and cooperating angle may be such that actuation of the bolt by the unlocking torque over a range of movement required to align the bolt lugs with the spaces between the barrel-extension lugs actuate the bolt to move axially with a first force provided by the unlocking torque and cooperating actuation surfaces of the bolt and barrel extension.

20. The bolt and barrel extension of any one of the preceding claims wherein the bolt lugs also define rearward-facing surfaces and the barrel-extension lugs define forward facing surfaces, wherein said forward rearward and forward facing surfaces conform to a helix and wherein the rearward and forward facing surfaces cooperate to actuate the bolt forwards when a torque is applied towards locking the bolt.

21. The bolt and barrel extension of claim 20 wherein the rearward-facing surfaces of the bolt and forward-facing surfaces of the barrel extension are dimensioned to pre-load the bolt lugs as a torque sufficient to lock the bolt is applied to the bolt.

21. The bolt and barrel extension of claim 20 wherein the rearward-facing surfaces of the bolt 5 and forward-facing surfaces of the barrel extension are dimensioned to pre-stress the bolt lugs as a torque sufficient to lock the bolt is applied to the bolt.

22. The bolt and barrel extension assembly of any one of claims 1 to 22 wherein the forward- facing surface of the bolt lugs and cooperating rear-facing surfaces on the barrel extension lugs may be arranged to conform to a helix.

23. The bolt and barrel extension assembly of any one of claims 1 to 22 wherein the forward-facing surfaces of the bolt lugs and the rear-facing surfaces of the barrel-extension lugs provide a cylindrical cam mechanism.

24. The bolt and barrel extension assembly of any one of claims 1 to 23 wherein the assembly is operable to have first and second modes of actuation towards extraction of a cartridge, wherein in a first mode the bolt is actuated rotationally and axially guided by the forward-facing surfaces of the bolt lugs and cooperating rear-facing surfaces of barrel extension lugs towards primary extraction of a cartridge by an extractor actuated by the bolt and wherein in a second mode the bolt moves purely axially with bolt lugs aligned with spaces between barrel-extension lugs to allow secondary extraction of the cartridge.

25. A firearm barrel extension for use with a bolt of a firearm, the barrel extension having a forward end and a rear end, the barrel extension also having a set of barrel-extension lugs arranged about the internal circumference of the barrel extension to be engaged by bolt lugs in use to lock the bolt, wherein spaces about the internal circumference of the barrel extension are defined between barrel extension lugs in which bolt lugs are able to move to allow the bolt to extract a cartridge from the barrel extension, wherein the barrel extension lugs define rear- facing surfaces arranged to conform to a helix to cause bolt lugs bearing against said reward- facing surfaces to convert a torque applied to the bolt to unlock the bolt, the torque converted to an axial component of force on the bolt towards the rear of the firearm.

26. A firearm barrel having a set of barrel lugs arranged about an internal circumference, wherein the lugs define a helical groove.

27. The firearm barrel of claim 26 wherein the groove provides a cam groove.

28. A firearm bolt for use with a barrel extension having rear-facing surfaces which conform to a helix, the bolt having bolt lugs with forward-facing surfaces to bear against said rear-facing surfaces to convert torque on the bolt suitable to unlock the bolt to an axial component of force.

27. A firearm bolt having a set of bolt lugs arranged about an external circumference, wherein the lugs define a helical groove.

28. The firearm bolt of claim 27 wherein the groove provides a cam groove.

29. The bolt of claim 16 having a set of bolt lugs arranged about a circumference of the bolt wherein a helical cam groove is defined by the bolt lugs.

30. A bolt and barrel extension assembly for a gas operated firearm operable to lock by aligning 5 bolt lugs with barrel-extension lugs and unlock by aligning bolt lugs with spaces defined between barrel-extension lugs and comprising a cam pin to rotate the bolt relative to the barrel extension, wherein the bolt provides primary extraction of a cartridge by converting rotational movement of the bolt to axial movement of the bolt with forward facing surfaces of bolt lugs bearing against rearward-facing surfaces on the barrel-extension lugs. The bolt may move to provide secondary extraction with bolt lugs aligned with spaces defined between barrel- extension lugs.

31. A bolt and barrel extension assembly for a firearm having a forward end and a rear end the assembly having a set of bolt lugs arranged about the circumference of the bolt and a set of barrel-extension lugs arranged about the internal circumference of the barrel extension, wherein the assembly has an unlocked configuration in which the bolt lugs are aligned with spaces defined between barrel extension lugs and the bolt is able to move rearwardly, and a locked configuration in which the bolt lugs are aligned with the bolt lugs, and wherein the bolt comprises a bore for a cam pin operable to receive an unlocking torque to actuate the bolt towards the unlocked configuration, and wherein the bolt lugs and barrel-extension lugs are arranged to provide a cylindrical cam mechanism capable of converting the unlocking torque on the bolt to an axial force on the bolt.

32. The bolt and barrel extension assembly of claim 31 wherein the bolt lug may define a cam groove.

33. The bolt and barrel extension assembly of claim 32 wherein the cam groove may conform to a helix.

34. The bolt and barrel extension assembly of claim 32 wherein the cam groove may be arranged to conform to a spiral.

35. The bolt and barrel extension assembly of any one of claims 1 to 34 wherein a barrel extension lug may define an actuation slider operable to slide through the cam groove to convert an unlocking torque to an axial force on the bolt relative to the barrel extension or barrel.

36. The bolt and barrel extension assembly of any one of claims 1 to 36 wherein the set of bolt lugs may define a cam groove extending through the set of bolt lugs.

37. The bolt and barrel extension assembly of any one of claims 1 to 36 wherein the set of barrel extension lugs may define a set of actuation sliders received in a cam groove defined by the set of barrel lugs to convert the unlocking torque on the bolt relative to the barrel extension to an axial force on the bolt relative to the barrel extension.

37. The bolt and barrel extension assembly of any one of claims 1 to 36 wherein the cam groove may be dimensioned to convert the unlocking torque received over a range sufficient to unlock the bolt to an axial force sufficient for primary extraction of a cartridge engaged by an extractor. 5 38. The bolt and barrel extension assembly of any one of claims 1 to 37 wherein the cam groove may be dimensioned to convert the unlocking torque received over a range sufficient to unlock the bolt to an axial force over a distance sufficient for primary extraction of a cartridge engaged by an extractor.

39. The bolt and barrel extension assembly of any one of claims 1 to 38 wherein the assembly may have first and second modes of actuation towards extraction of a cartridge, wherein in a first mode the bolt moves rotationally and axially as guided by the cam mechanism towards primary extraction of a cartridge by an extractor associated with the bolt and wherein in a second mode the bolt moves purely axially with bolt lugs aligned with spaces between barrel- extension lugs to allow secondary extraction of the cartridge.

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